Characterization of a Novel Polymeric Bioflocculant Produced from Bacterial Utilization of n-Hexadecane and Its Application in Removal of Heavy Metals

Efficacy of exopolysaccharide in dye-laden wastewater treatment: A comprehensive review

The discharge of dye-laden wastewater into the water streams causes severe water and soil pollution, which poses a global threat to aquatic ecosystems and humans. A diverse array of microorganisms such as bacteria, fungi, and algae produce exopolysaccharides (EPS) of different compositions and exhibit great bioflocculation potency to sustainably eradicate dyes from water bodies. Nanomodified chemical composites of EPS enable their recyclability during dye-laden wastewater treatment. Nevertheless, the selection of potent EPS-producing strains and physiological parameters of microbial growth and the remediation process could influence the removal efficiency of EPS. This review will intrinsically discuss the fundamental importance of EPS from diverse microbial origins and their nanomodified chemical composites, the mechanisms in EPS-mediated bioremediation of dyes, and the parametric influences on EPS-mediated dye removal through sorption/bioflocculation. This review will pave the way for designing and adopting futuristic green and sustainable EPS-based bioremediation strategies for dye-laden wastewater in situ and ex situ.

Isolation and characterization of Stenotrophomonas pavanii GXUN74707 with efficient flocculation performance and application in wastewater treatment

The identification of microorganisms with excellent flocculants-producing capability and optimization of the fermentation process are necessary for the wide-scale application of bioflocculants. Therefore, we isolated and identified a highly efficient flocculation performance strain of Stenotrophomonas pavanii GXUN74707 from the sludge. The optimal fermentation and flocculation conditions of strain S. pavanii GXUN74707 was in fermentation medium with glucose and urea as the carbon and nitrogen sources, respectively, at pH 7.0 for 36 h, which treatment of kaolin suspension with 0.5 mL of the fermentation broth resulted in a flocculation rate of 99.0%. The bioflocculant synthesized by strain S. pavanii GXUN74707 was found mainly in the supernatant of the fermentation broth. Chemical analysis revealed that the pure bioflocculant consisted of 79.70% carbohydrates and 14.38% proteins. The monosaccharide components of MBF-GXUN74707 are mainly mannose (5.96 μg/mg), galactose (1.86 μg/mg), and glucose (1.73 μg/mg). Infrared spectrometric analysis showed the presence of carboxyl (COO-), hydroxyl (-OH) groups. The SEM images showed clumps of rod-shaped bacteria with adhesion of extracellular products. Furthermore, the strain decolored dye wastewater containing direct black, direct blue, and Congo red by 89.2%, 95.1%, 94.1%, respectively. The chemical oxygen demand (COD) and biological oxygen demand (BOD) removal rates after treatment of aquaculture wastewater with the fermentation broth were 68% and 23%, respectively. This study is the first to report the performance and application of strain Stenotrophomonas pavanii in wastewater flocculation. The results indicate that strain S. pavanii is a good candidate for the production novel bioflocculants and demonstrates its potential industrial practicality in biotechnology processes.

Sustainable production of bacterial flocculants by nylon-6,6 microplastics hydrolysate utilizing Brucella intermedia ZL-06

Nylon-6,6 microplastics (NMPs) in aquatic systems have emerged as potential contaminants to the global environment and have garnered immense consideration over the years. Unfortunately, there is currently no efficient method available to eliminate NMPs from sewage. This study aims to address this issue by isolating Brucella intermedia ZL-06, a bacterium capable of producing a bacterial polysaccharide-based flocculant (PBF). The PBF generated from this bacterium shows promising efficacy in effectively flocculating NMPs. Subsequently, the precipitated flocs (NMPs + PBF) were utilized as sustainable feedstock for synthesizing PBF. The study yielded 6.91 g/L PBF under optimum conditions. Genome sequencing analysis was conducted to study the mechanisms of PBF synthesis and nylon-6,6 degradation. The PBF exhibited impressive flocculating capacity of 90.1 mg/g of PBF when applied to 0.01 mm NMPs, aided by the presence of Ca2+. FTIR and XPS analysis showed the presence of hydroxyl, carboxyl, and amine groups in PBF. The flocculation performance of PBF conformed to Langmuir isotherm and pseudo-first-order adsorption kinetics model. These findings present a promising approach for reducing the production costs of PBF by utilizing NMPs as sustainable nutrient sources.

Production of bioflocculant from Klebsiella pneumoniae: evaluation of fish waste extract as substrate and flocculation performance

The bioflocculant producing bacterial strain - UKD24 was isolated from the domestic sewage treatment plant. The isolated strain was identified as Klebsiella pneumoniae by using 16S rRNA gene sequencing. The K. pneumoniae UKD24 showed remarkable flocculation rates when grown with the carbon sources namely glucose, sucrose and lactose, and many commercial nitrogen sources. Furthermore, the fish waste extract (FE) was used to enhance the productivity of the bioflocculant as a nitrogen supplement and it showed a significant level of flocculation rate similar to the commercial nitrogen sources. The Box-Behnken experiments were designed to predict the optimal conditions for bioflocculant production and it suggested that glucose - 3.247 g L-1, FE - 0.5 g L-1 and inoculum size - 1% are the suitable levels for bioflocculant production. The FTIR analysis of the bioflocculant showed the functional groups related to the polysaccharides and the EEM analysis showed the fluorescence components related to the proteins and humic acids. The biochemical composition of the bioflocculant was identified as polysaccharides (24.36 ± 1.5%) and protein (12.15 ± 0.2%). The tested optimum conditions of the bioflocculant to induce flocculation were tested in the kaolin wastewater and it showed that the optimum dosage of the flocculant was 5 mg L-1 and the pH range was broad as 5-10. The cation dependency tests revealed that the monovalent and divalent cations are highly suitable for flocculation while the trivalent cations showed moderate flocculation. The Cr(VI) removal efficiency of the bioflocculant showed that ∼35% of heavy metal is trapped into flocks during the flocculation.

The Large Molecular Weight Polysaccharide from Wild Cordyceps and Its Antitumor Activity on H22 Tumor-Bearing Mice

Cordyceps has anti-cancer effects; however, the bioactive substance and its effect are still unclear. Polysaccharides extracted from Cordyceps sinensis, the fugus of Cordyceps, have been reported to have anti-cancer properties. Thus, we speculated that polysaccharides might be the key anti-tumor active ingredients of Cordyceps because of their larger molecular weight than that of polysaccharides in Cordyceps sinensis. In this study, we aimed to investigate the effects of wild Cordyceps polysaccharides on H22 liver cancer and the underlying mechanism. The structural characteristics of the polysaccharides of WCP were analyzed by high-performance liquid chromatography, high-performance gel-permeation chromatography, Fourier transform infrared spectrophotometry, and scanning electron microscopy. Additionally, H22 tumor-bearing BALB/c mice were used to explore the anti-tumor effect of WCP (100 and 300 mg/kg/d). The mechanism by WCP inhibited H22 tumors was uncovered by the TUNEL assay, flow cytometry, hematoxylin-eosin staining, quantitative reverse transcription-polymerase chain reaction, and Western blotting. Here, our results showed that WCP presented high purity with an average molecular weight of 2.1 × 10⁶ Da and 2.19 × 10⁴ Da. WCP was determined to be composed of mannose, glucose, and galactose. Notably, WCP could inhibit the proliferation of H22 tumors not only by improving immune function, but also by promoting the apoptosis of tumor cells, likely through the IL-10/STAT3/Bcl2 and Cyto-c/Caspase8/3 signaling pathways, in H22 tumor-bearing mice. Particularly, WCP had essentially no side effects compared to 5-FU, a common drug used in the treatment of liver cancer. In conclusion, WCP could be a potential anti-tumor product with strong regulatory effects in H22 liver cancer.

Production and characterization of a bioflocculant produced by Proteus mirabilis AB 932526.1 and its application in wastewater treatment and dye removal

Microbial flocculants affect the aggregation of suspended solutes in solutions, thus, they are a viable alternative to inorganic and organic synthetic flocculants which are associated with deleterious health problems. Moreover, a potential solution for wastewater treatment. The study aimed to produce and characterize a bioflocculant from Proteus mirabilis AB 932526.1 and apply it in domestic wastewater treatment and dye removal. The bioflocculant was extracted using butanol and chloroform (5:2 v/v). Carbohydrates, proteins, and uronic acid were identified using phenol-sulphuric acid, Bradford, and Carbazole essays. The morphology, crystallinity and elemental composition of the purified bioflocculant were determined using a Scanning electron microscope (SEM), X-ray diffraction analysis and SEM energy dispersive elemental detector (SEM-EDX). The antimicrobial properties and dye removal efficiencies were evaluated. About 3.8 g/L yields of the purified bioflocculant were attained. Chemical composition analysis revealed the presence of 65 % carbohydrates, 10 % proteins, and 24 % uronic acids. The bioflocculant displayed an amorphous and crystalline structure. Bioflocculant further shows some remarkable properties as they can be able to inhibit the growth of both Gram-positive and Gram-negative microorganisms. The removal efficiencies of 85 % (COD), 82 % (BOD), and 81 % (SO4 2−) in domestic wastewater were achieved. Moreover, the high removal efficiency of staining dyes such as methylene blue (71 %), carbol fuchsin (81 %), safranin (83 %), methylene orange (90 %), and Congo red (90 %) were found. The produced bioflocculant can imply industrial applicability.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.

Production and Characterization of a Bioflocculant from Pichia kudriavzevii MH545928.1 and Its Application in Wastewater Treatment

A variety of flocculants have been used to aggregate colloidal substances. However, recently, owing to the adverse effects and high costs of conventional flocculants, natural flocculants such as microbial flocculants are gaining attention. The aim of the study was to produce and characterize a bioflocculant from Pichia kudriavzevii MH545928.1 and apply it in wastewater treatment. A mixture of butanol and chloroform (5:2 v/v) was used to extract the bioflocculant. Phenol–sulphuric acid, Bradford and Carbazole assays were utilized for the identification of carbohydrates, proteins and uronic acid, respectively. Scanning electron microscopy (SEM) and elemental detector were employed to determine the surface morphology and elemental compositions. The removal efficiencies were 73%, 49% and 47% for BOD, COD and P, respectively. The bioflocculant (2.836 g/L) obtained showed the presence of carbohydrates (69%), protein (11%) and uronic acid (16%). The bioflocculant displayed a cumulus-like structure and the elemental composition of C (16.92%), N (1.03%), O (43:76%), Na (0.18%), Mg (0.40%), Al (0.80%), P (14.44%), S (1.48%), Cl (0.31%), K (0.34%) and Ca (20.35). It showed the removal efficiencies of 43% (COD), 64% (BOD), 73% (P) and 50% (N) in coal mine wastewater. This bioflocculant is potentially viable to be used in wastewater treatment.

Transcriptome analysis of potential flocculation-related genes in Streptomyces sp. hsn06 with flocculation activity on Chlorella vulgaris biomass

Chlorella vulgaris is a biomass energy provider with promising potential to help alleviate the energy crisis. Streptomyces sp. hsn06, as an actinomycete, can harvest C. vulgaris biomass safely and efficiently through flocculation activity, and proteins contribute greatly to the flocculation effect. However, potential flocculation protein-related genes are unclear. The mycelia of strain hsn06 after culture with glucose as the sole carbon source exhibited significantly higher flocculation activity as well as higher protein contents than those cultured with starch as the carbon source. To further explore the flocculation mechanism, the mycelia of strain hsn06 with distinct flocculation activities after culture with different carbon sources were examined by transcriptome analysis. We found that 403 genes were differentially up-regulated in mycelia cultured with glucose, compared to those cultured with starch as the carbon source. Five significantly differentially expressed protein-related genes were determined and confirmed by qRT-PCR, which indicated that three of the selected genes were potential flocculation-related genes. These results advance our understanding of potential flocculation-related genes during the harvesting of microalgal biomass.

Isolation and Optimization of Culture Conditions of a Bioflocculant-Producing Fungi from Kombucha Tea SCOBY

Biolocculants are gaining attention in research due to their environmental friendliness and innocuousness to human in comparison to the conventional flocculants. The present study aimed to investigate the ability of fungi from Kombucha tea SCOBY to produce effective bioflocculant in bulk. A 16S rRNA gene sequence analysis was utilized to identify the isolate. The medium composition (carbon and nitrogen sources) and culture conditions (inoculum size, temperature, shaking speed, pH, and time) were optimized using one-factor-at-a-time method. The functional groups, morphology, and crystallinity of the bioflocculant were evaluated using Fourier transform infrared (FT-IR), scan electron microscope (SEM) and X-ray diffractometry (XRD). The fungus was found to be Pichia kudriavzevii MH545928.1. It produced a bioflocculant with flocculating activity of 99.1% under optimum conditions; 1% (v/v) inoculum size, glucose and peptone as nutrient sources, 35 °C, pH 7 and the shaking speed of 140 rpm for 60 h. A cumulus-like structure was revealed by SEM; FT-IR displayed the presence of hydroxyl, carboxyl, amine, and thiocynates. The XRD analysis demonstrated the bioflocculant to have big particles with diffraction peaks at 10° and 40° indicating its crystallinity. Based on the obtained results, P. kudriavzevii MH545928.1 has potential industrial applicability as a bioflocculant producer.

Enlightening the characteristics of bioflocculant of endophytic actinomycetes from marine algae and its biosorption of heavy metal removal

The removal of toxic heavy metal ions from contaminated environments is a great challenge and requires an alternative rapid, efficient, economical bioremediation approach. Henceforth, bioflocculant producing endophytic actinobacterial sp. was isolated from heavy metal contaminated marine environments for heavy metal biosorption process. After molecular characterization, the isolated actinomycete starin was Nocardiopsis sp. GRG 3 (KT235642). It was indicated that the maximum flocculating activity of 80.90% with glucose, and yield is 4.52 g L¹. The optimum flocculating activity was reached at pH 7 in the presence of CaCl₂ ions. Further, the bioflocculent produced Nocardiopsis sp. GRG 3 (KT235642) was characterized by fourier transform infrared analysis spectra (FTIR) and displayed the presence of carboxyl, hydroxyl, amino groups and characteristic of more polysaccharide and protein. The heavy metal sorption by bioflocculant Nocardiopsis sp. GRG 3 (KT235642) was effectively removed 55.90% Cd, 85.90% Cr, 74.7% Pb, and 51.90% Hg. Therefore, this study was proved that the bioflocculant derived from endophytic actinobacteria, Nocardiopsis sp. GRG 3 (KT235642) as a effective alternative method for decreasing the heavy metals towards sustainable environmental management.

Recent advances and perspectives in efforts to reduce the production and application cost of microbial flocculants

Microbial flocculants are macromolecular substances produced by microorganisms. Due to its non-toxic, harmless, and biodegradable advantages, microbial flocculants have been widely used in various industrial fields, such as wastewater treatment, microalgae harvest, activated sludge dewatering, heavy metal ion adsorption, and nanoparticle synthesis, especially in the post-treatment process of fermentation with high safety requirement. However, compared with the traditional inorganic flocculants and organic polymeric flocculants, the high production cost is the main bottleneck that restricts the large-scale production and application of microbial flocculants. To reduce the production cost of microbial flocculant, a series of efforts have been carried out and some exciting research progresses have been achieved. This paper summarized the research advances in the last decade, including the screening of high-yield strains and the construction of genetically engineered strains, search of cheap alternative medium, the extraction and preservation methods, microbial flocculants production as an incidental product of other biological processes, combined use of traditional flocculant and microbial flocculant, and the production of microbial flocculant promoted by inducer. Moreover, this paper prospects the future research directions to further reduce the production cost of microbial flocculants, thereby promoting the industrial production and large-scale application of microbial flocculants.

Energy-saving preparation of a bioflocculant under high-salt condition by using strain Bacillus sp. and the interaction mechanism towards heavy metals

A highly efficient bioflocculant, i.e., Na-Bsp was successfully prepared by using a tolerant strain-Bacillus sp. under high-salt condition without sterilization. Salt-containing medium was not infected by other strains throughout the whole incubation period in 168 h. The as-prepared Na-Bsp was found to be cation-dependent, exhibiting high flocculant efficiency (FE) i.e., 97.69 ± 0.61%, towards kaolin particles by aid of Fe³⁺. High FE values were well maintained under a wide pH range and/or boiled water treatment, likely because of the main constituent of polysaccharide. The presence of hydroxyl, carboxyl, and amine groups on the bioflocculant surface were possibly responsible for strong interactions with heavy metals. The adsorption capacities of Pb²⁺, Cu²⁺ and Cr⁶⁺ were 1000.0, 434.8 and 384.6 mg g^-1, respectively. The changing of structure and configuration of bioflocculant during the metal adsorption were explored by the scanning electron microscope with electron energy loss spectroscopy and three-dimensional excitation-emission fluorescence spectrometry. This study provided a novel production method, whereby the conventional sterilization could be avoided, which is of great environmental significance for steam-saving. Furthermore, the as-prepared Na-Bsp exhibited high adsorption capacities toward heavy metals, which sheds lights on its potential usage as an alternative adsorbent.

Application of isolated halophilic microorganisms suspended and immobilized on walnut shell as biocarrier for treatment of oilfield produced water

Salinity expressed as total dissolved solids (TDS), is the most challenging parameter in bioremediation of produced water which may inhibit the microbial activities and cause sedimentation problems. The present study explores the feasibility of using walnut shell as an inexpensive and accessible adsorbent-carrier for the immobilization of isolated halophilic microorganisms for treatment of synthetic oilfield produced water. The moving bed biofilm reactor (MBBR) was examined with influent chemical oxygen demand (COD) concentrations from 900 to 3600 mg L^-1, TDS concentrations from 35,000-200,000 mg L^-1, and cycle times from 24 to 72 h. Comparison of the MBBR with the conventional sequencing batch reactor (SBR) indicated that both systems operated at lower influent COD and TDS concentrations satisfactorily; but at higher TDSs (above 150,000 mg L^-1) the MBBR was more resistant to the shocks of toxicity (salinity) and organic load relative to the SBR. Also, the effluent turbidity was lower and the free sludge settling property was more favorable in the MBBR with average sludge volume index (SVI) of 38.8 mL g^-1 compared to the SBR with SVI of 98.09 mL g^-1. Microbial identification confirmed the presence of eight dominant halophilic species which were hydrocarbon degraders and/or denitrifiers.

Marine Actinobacteria Bioflocculant: A Storehouse of Unique Biotechnological Resources for Wastewater Treatment and Other Applications

The bioactive compounds produced by actinobacteria have played a major role in antimicrobials, bioremediation, biofuels, enzymes, and anti-cancer activities. Biodegradable microbial flocculants have been produced by bacteria, algae, and fungi. Microbial bioflocculants have also attracted biotechnology importance over chemical flocculants as a result of degradability and environmentally friendly attributes they possess. Though, freshwater actinobacteria flocculants have been explored in bioflocculation. Yet, there is a paucity of information on the application of actinobacteria flocculants isolated from the marine environment. Similarly, marine habitats that supported the biodiversity of actinobacteria strains in the field of biotechnology have been underexplored in bioflocculation. Hence, this review reiterates the need to optimize culture conditions and other parameters that affect bioflocculant production by using a response surface model or artificial neural network.

Recent Achievements in Polymer Bio-Based Flocculants for Water Treatment

Polymer flocculants are used to promote solid-liquid separation processes in potable water and wastewater treatment. Recently, bio-based flocculants have received a lot of attention due to their superior advantages over conventional synthetic polymers or inorganic agents. Among natural polymers, polysaccharides show many benefits such as biodegradability, non-toxicity, ability to undergo different chemical modifications, and wide accessibility from renewable sources. The following article provides an overview of bio-based flocculants and their potential application in water treatment, which may be an indication to look for safer alternatives compared to synthetic polymers. Based on the recent literature, a new approach in searching for biopolymer flocculants sources, flocculation mechanisms, test methods, and factors affecting this process are presented. Particular attention is paid to flocculants based on starch, cellulose, chitosan, and their derivatives because they are low-cost and ecological materials, accepted in industrial practice. New trends in water treatment technology, including biosynthetic polymers, nanobioflocculants, and stimulant-responsive flocculants are also considered.

Production of a bioflocculant from ramie biodegumming wastewater using a biomass-degrading strain and its application in the treatment of pulping wastewater

The major bottleneck for industrial applications of microbial flocculants is the high production cost. Here, a novel bacterium, Diaphorobacter nitroreducens R9, was isolated that can secret ligninase and cellulase and simultaneously produce bioflocculants (MBF-9) through conversion of ramie biomass. The production of MBF-9 was closely related to the ligninase and cellulase activities of D. nitroreducens. Both ligninase and cellulase showed peak activity at pH 8.5 and 6.0 and retained approximately 80% of cellulase activity and 95% of ligninase activity at pH 8.0. The optimal production conditions with the highest bioflocculant yield (3.86 g/L degumming wastewater) were determined at a fermentation time of 48 h, fermentation temperature of 30 °C, inoculum size of 4.0%, COD_Cr of ramie degumming wastewater of 1500 mg/L and initial pH of 8.0. In addition, MBF-9 removed 96.2% turbidity, 79.5% chemical oxygen demand (COD), 59.2% lignin, and 63.1% sugar from the pulping wastewater at an MBF-9 dosage of 831.57 mg/L.

Unravelling the characteristics of a heteropolysaccharide-protein from an Haloarchaeal strain with flocculation effectiveness in heavy metals and dyes removal

The production, characterization and potential application in heavy metals and dyes removal of a novel heteropolysaccharide-protein named, gpHb, produced by an Haloarchaeal strain Halogeometricum borinquense strain A52 were investigated. The highest gpHb yield of 13.96 ± 0.32 g/L was produced under optimized conditions by response surface methodology. We focused on the characteristics and flocculation performance of gpHb. An important attribute of protein with 16 protein types identified that occupied a total content of 50.2% in the gpHb. Additionally, carbohydrate that occupied 30.4% of the total bioflocculant content consisted of three monosaccharides. Fourier transform-infrared spectroscopy indicated the presence of carboxyl, hydroxyl, amine, amide, and sulphate groups. To further study flocculation activities, factors such as bioflocculant dosage, temperature, pH, salinity and cations addition were tested. In comparison to the chemical flocculant polyaluminium chloride, gpHb maintain high activity at large range of salinity and its flocculation activity was higher on both sides of pH 7. Addition of trivalent cation mainly Fe³⁺ enhances the flocculating rate indicating that the bioflocculant is negatively charged. Its practical applicability was established for heavy metals and dyes removal from saline aqueous solutions. The highest removal efficiency was observed with Cr³⁺ (91.4%) and Ni²⁺ (89.60%) and with basic blue 3 (83.8%) and basic red (78.6%). The excellent flocculation activity of gpHb under saline condition suggests its potential industrial utility for treatment of textile and tannery wastewaters.

Bioconversion of citrus peel wastes into bioflocculants and their application in the removal of microcystins

In this study, the mechanism for converting citrus peel wastes (CPW) into bioflocculants using Alcaligenes faecalis subsp. phenolicus ZY-16 was analysed. The results demonstrated that the ZY-16 strain could produce various lignocellulolytic enzymes, containing cellulase, hemicellulase, pectinase, protease, and ligninase, enhancing the hydrolysis of citrus peel wastes. Molecular distillation removes antimicrobial limonene, which could inhibit bioflocculant production. The optimal fermentation conditions with the highest bioflocculant yield (3.49 g/L) were 38.79 g/L of CPW, 35.54 °C, and pH 4.48. Furthermore, the bioflocculant was used to eliminate microcystins for the first time, and the highest removal efficiency (90.05%) was achieved at a pH of 3.0, after 800 mg/L of bioflocculant was added into the microcystins solution (10 mg/L) for 60 min. Therefore, this paper demonstrated that CPW could be a cost-effective feedstock for the production of bioflocculants, which have potential application in microcystin removal.

Bioflocculant production using palm oil mill and sago mill effluent as a fermentation feedstock: Characterization and mechanism of flocculation

This study was conducted to examine the production of bioflocculants using agricultural wastewater as a fermentation feedstock under different temperatures and incubation times. The mechanism of flocculation was studied to gain a detailed understanding of the flocculation activity. The highest bioflocculant yield (2.03 g/L) at a temperature of 40 °C was produced in a palm oil mill effluent medium (BioF-POME). Bioflocculant produced from a fermented SME medium (BioF-SME) showed the highest activity. The flocculation tests for colour and turbidity removal from lake water indicated that BioF-SME and BioF-POME performed comparably to commercial alum. Analyses of the bioflocculants using liquid chromatography-mass spectrometry (LC-MS) found that the bioflocculants contained xylose and glucose. The mechanism study showed that flocculation occurred through charge neutralization and interparticle bridging between the bioflocculant polymer and the particles in the lake water. Thus, agricultural wastewater can be used as a fermentation feedstock for high-quality bioflocculants.

Simultaneous nitriles degradation and bioflocculant production by immobilized K. oxytoca strain in a continuous flow reactor

High cost is one of the limiting factors in the industrial production of bioflocculant. Simultaneous preparation of bioflocculant from the contaminants in wastewater was considered as a potential approach to reduce the production cost. In this study, butyronitrile and succinonitrile were verified as sole nitrogen sources for the growth of strain K. oxytoca GS-4-08 in batch experiments. Moreover, more than 90 % of the mixed nitriles could be degraded in a continuous flow reactor, and the bioflocculant could be prepared simultaneously in the effluent. All the as-prepared bioflocculants exhibited high flocculation efficiencies of over 90 % toward Kaolin solution. FTIR and XPS results further unveiled that, the bioflocculant samples with abundance of carboxyl, amine and hydroxyl groups may play an important role on adsorption of Pd²⁺. The adsorption process could be well simulated by Freundlich model, and the K_f values were as high as 452.8 mg^1-1/n l^1/n g^-1. The results obtained in this study not only confirm the technical feasibility for preparation of bioflocculant from various single nitrile and/or mixed nitriles, but also promise its economic feasibility.

A cost-effective and environmentally sustainable process for phycoremediation of oil field formation water for its safe disposal and reuse

High volumes of formation water comprising of complex mixture of hydrocarbons is generated during crude oil exploration. Owing to ecotoxicological concerns, the discharge of the formation water without remediation of hydrocarbonaceous pollutants is not permitted. Keeping this into mind, we carried out phycoremediation of hydrocarbons in formation water so that it can be safely discharged or re-used. For this, a native algal species was isolated from formation water followed by its morphological and 18S ribosomal RNA based identification confirming the algal isolate to be Chlorella vulgaris BS1 (NCBI GenBank Accession No. MH732950). The algal isolate exhibited high biomass productivity of 1.76 gm L⁻¹ d⁻¹ (specific growth rate: 0.21 d⁻¹, initial inoculum: 1500 mg L⁻¹) along with remediation of 98.63% petroleum hydrocarbons present in formation water within 14 days of incubation indicating an efficient hydrocarbon remediation process. Concomitantly, the hydrocarbon remediation process resulted in reduction of 75% Chemical Oxygen Demand (COD) load and complete removal of sulfate from formation water making it suitable for safe disposal or reuse as oil well injection water respectively. The present process overcomes the bottlenecks of external growth nutrient addition or dilution associated with conventional biological treatment resulting in a practically applicable and cost-effective technology for remediation of oil field formation water.

Bioconversion of kitchen wastes into bioflocculant and its pilot-scale application in treating iron mineral processing wastewater

In this study, the feasibility of converting kitchen waste into bioflocculant using Bacillus agaradhaerens C9 was analyzed. The result showed that strain C9 could secrete various degrading enzymes, including amylase, protease, lipase, cellulase, xylanase and pectinase, promoting the hydrolysis of kitchen waste. Strong alkaline fermentation condition was able to induce the bioflocculant production, and inhibit the growth of contaminated bacteria, which avoids the sterilization process of kitchen waste. The optimum fermentation condition for enzymatic hydrolysis and bioflocculant production was 40 g/L kitchen waste, 37 °C, pH 9.5, and the highest bioflocculant yield of 6.92 g/L was achieved. Furthermore, bioflocculant was applied to treat pilot-scale (30 L) of mineral processing wastewater for the first time, and the removal rate of 92.35% was observed when 9 mg/L bioflocculant was added into wastewater. Therefore, this study could promote the resource utilization of kitchen waste and recycling of mineral processing wastewater.

Bioflocculant production and heavy metal sorption by metal resistant bacterial isolates from gold mining soil

Two bioflocculant producing bacterial isolates from mining soil samples were investigated for their application in heavy metal removal. The bacterial isolates were identified as Pseudomonas koreensis and Pantoea sp. using 16S rRNA gene. Cadmium resistant genes cadA and CzcD were detected in Pantoea sp. while P. koreensis harbor CzcD and chrA responsible for Cd and Cr resistance respectively. The isolates showed maximum flocculating activity of 71.3% and 51.7% with glucose and yield of 2.98 g L^-1 and 3.26 g L^-1 for Pantoea sp. and P. koreensis respectively. The optimum flocculating activity was achieved at pH 7.5 and temperature of 30 °C. Fourier transform infrared analysis of the bioflocculants produced by the two isolates showed the presence of carboxyl, hydroxyl and amino groups characteristic of polysaccharide and protein. Heavy metal sorption by bioflocculant of Pantoea sp. removed 51.2% Cd, 52.5% Cr and 80.5% Pb while that of P. koreensis removed 48.5% Cd, 42.5% Cr and 73.7% Pb. The bioflocculants produced have potential in metal removal from industrial wastes.

A novel efficient bioflocculant QZ-7 for the removal of heavy metals from industrial wastewater

In this study, a novel bioflocculant QZ-7 was produced from Bacillus salmalaya 139SI for industrial wastewater treatment. Biochemical analysis, FTIR, scanning electron microscopy-energy dispersive X-ray spectroscopy, and thermogravimetric analysis were performed. A synthetic wastewater sample was used to validate the performance of the prepared OZ-7 for the adsorption efficiency of As, Zn²⁺ Pb²⁺, Cu²⁺, and Cd²⁺ under optimal experimental conditions such as initial metal concentrations, pH, contact time (h) and QZ-7 adsorbent dosage (mg mL⁻¹). The maximum removal efficiency for Zn²⁺ (81.3%), As (78.6%), Pb²⁺ (77.9%), Cu²⁺ (76.1%), and Cd²⁺ (68.7%) was achieved using an optimal bioflocculant dosage of 60 mg L⁻¹ at 2 h shaking time, 100 rpm and pH 7. Furthermore, the obtained optimum experimental conditions were validated using real industrial wastewater and the removal efficiencies of 89.8%, 77.4% and 58.4% were obtained for As, Zn²⁺ and Cu²⁺, respectively. The results revealed that the prepared bioflocculant QZ-7 has the capability to be used for the removal of heavy metals from industrial wastewater.

In this study, a novel bioflocculant was produced using Bacillus salmalaya 139SI for industrial waste water treatment.

Microbial Flocculants as an Alternative to Synthetic Polymers for Wastewater Treatment: A Review

Microorganisms such as bacteria, fungi, and microalgae have been used to produce bioflocculants with various structures. These polymers are active substances that are biodegradable, environmentally harmless, and have flocculation characteristics. Most of the developed microbial bioflocculants displayed significant flocculating activity (FA > 70–90%) depending on the strain used and on the operating parameters. These biopolymers have been investigated and successfully used for wastewater depollution in the laboratory. In various cases, selected efficient microbial flocculants could reduce significantly suspended solids (SS), turbidity, chemical oxygen demand (COD), total nitrogen (Nt), dye, and heavy metals, with removal percentages exceeding 90% depending on the bioflocculating materials and on the wastewater characteristics. Moreover, bioflocculants showed acceptable results for sludge conditioning (accepted levels of dry solids, specific resistance to filtration, moisture, etc.) compared to chemicals. This paper explores various bioflocculants produced by numerous microbial strains. Their production procedures and flocculating performance will be included. Furthermore, their efficiency in the depollution of wastewater will be discussed.

Advances in exopolysaccharides based bioremediation of heavy metals in soil and water: A critical review

Extracellular polysaccharides or Exopolysaccharides (EPS) are extensively studied bacterial byproducts with high molecular weight attributed to several applications. In spite of their application in the field of food, pharmaceutical, nutraceutical, herbicidal and cosmeceutical industries they were well known for their efficiency in the bioremediation of water and soil tainted with heavy metals. These heavy metals are comparatively high in density than water and are involved in several biological processes. But slight increase in levels can create toxicological bias. The techniques like electrodialysis, chemical precipitation, ion exchange and membrane separation have a lot of disadvantages akin to high energy consumption, high cost, partial exclusion, and creation of poisonous mire. In this context, EPS has a top role to play in the bioremediation of heavy metals. This review gives the critical assessment of the extensive work done to deal this issue by different groups in the last five years. It also explains how different natural circumstances have attributed to the advancement of EPS production, thereby increasing the capacity of bioremediation to deal the issue of heavy metal contamination in both soil and water. A detailed discussion of the EPS formation by bacteria and fungi with their applicability was reported.

Bioflocculants' production in a biomass-degrading bacterium using untreated corn stover as carbon source and use of bioflocculants for microalgae harvest

BACKGROUND

Bioflocculation has been developed as a cost-effective and environment-friendly method to harvest multiple microalgae. However, the high production cost of bioflocculants makes it difficult to scale up. In the current study, low-cost bioflocculants were produced from untreated corn stover by a biomass-degrading bacterium Pseudomonas sp. GO2.

RESULTS

Pseudomonas sp. GO2 showed excellent production ability of bioflocculants through directly hydrolyzing various biomasses. The untreated corn stover was selected as carbon source for bioflocculants' production due to its highest flocculating efficiency compared to that when using other biomasses as carbon source. The effects of fermentation parameters on bioflocculants' production were optimized via response surface methodology. According to the optimal model, an ideal flocculating efficiency of 99.8% was obtained with the fermentation time of 130.46 h, initial pH of 7.46, and biomass content of 0.64%. The relative importance of carboxymethyl cellulase and xylanase accounted for 51.8% in the process of bioflocculants' production by boosted regression tree analysis, further indicating that the bioflocculants were mainly from the hydrolysates of biomass. Biochemical analysis showed that it contained 59.0% polysaccharides with uronic acid (34.2%), 32.1% protein, and 6.1% nucleic acid in the bioflocculants, which had an average molecular weight as 1.33 × 10⁶ Da. In addition, the bioflocculants showed the highest flocculating efficiency at a concentration of 12.5 mg L^-1 and were stable over broad ranges of pH and temperature. The highest flocculating efficiencies obtained for Chlorella zofingiensis and Neochloris oleoabundans were 77.9 and 88.9%, respectively.

CONCLUSIONS

The results indicated that Pseudomonas sp. GO2 can directly utilize various untreated lignocellulolytic biomasses to produce low-cost bioflocculants, which showed the high efficiency to harvest two green microalgae in a low GO2 fermentation broth/algal culture ratio.